1. Field of the Invention
The present invention relates to a substrate alignment mechanism and a substrate testing device having the substrate alignment mechanism and a substrate testing method, which is applicable to testing a TFT array substrate for use in flat panel displays such as a liquid crystal display or an organic EL display, for example.
2. Description of the Related Art
In the manufacturing process of flat panel displays such as liquid crystal display or organic EL display, a plurality of panels having a pattern of TFT array are usually formed on a glass substrate, and each panel is cut out from the glass substrate. In testing the flat panel displays, the glass substrate is tested, or the TFTs or pixels formed on the glass substrate are evaluated for the characteristics.
To test the TFT array formed on the substrate, the TFT array substrate is usually held on the stage.
In testing the TFT array, a repair operation is performed using the tested result, whereby it is required to determine a defect position accurately. Therefore, it is required that a substrate testing device locates a substrate to be tested at the same position every time. However, a substrate conveying mechanism such as a movable stage does not have an enough precision to meet the requirements. Though the mechanical alignment may be made to adjust the alignment, there is a limitation on the precision in the mechanical adjustment of alignment, whereby it is difficult to meet the necessary precision.
To make the alignment adjustment of the substrate, it is common that an alignment mark is provided on the substrate, and detected to determine the substrate position with respect to the substrate testing device. Since the substrate testing device with SEM tests the substrate employing the electron beam, the alignment mark may be detected by the scanning of the electron beam.
However, when the alignment mark is detected employing the electron beam, it may be difficult to detect the alignment mark accurately, depending on the material of the alignment mark. For example, when the alignment mark is made of an insulating material, there is a problem that the alignment mark is charged up due to irradiation with the electron beam, causing a failure such as discharge. Also, there is another problem that the alignment mark is difficult to distinguish from the substrate, because they are very close in the signal intensity and thereby the image contrast.